That made a trace, which ended up in the 'moko in ~/Maps (which is itself a link to my microSD card's FS). I copied that to ~/tmp on my desktop.
Following this page I downloaded the converter to ~/openmoko/convert2gpx.pl and ran
~/openmoko/convert2gpx.pl 20090810_080818.log > 20090810_080818.gpx
Ran josm with
java -jar ~/bin/josm.jarand used Open to open my track. Then also used Download OSM Data to get the existing OSM data for my area, using shift-click-drag to open a slightly bigger rectangle on the map so I could get both Sedgwick and Cavendish Streets to make sure that I connected both ends of the alley.
Used the node-connector to tag the three legs of the alley, pressing ESC after the last leg to dismiss the floating arrow.
Then used Select Move and Rotate Objects to select my new track, using Presets I tagged it as Streets -> Service, with a surface of "concrete" (as suggested by this page in the wiki).